Terminal Weevils

Terminal Weevils

General Biology of Terminal Weevils

Spruce Terminal Weevil

Hosts & Range

Biology / Life Cycle

Tree Response

Population Dynamics

Signs & Symptoms

Tree Resistance

Damage

Hazard Rating

Management

brushing

fertilizing

spacing

pruning

rehab

direct control

	leader clipping
	insecticides
	tree breeding

Pine Terminal Weevil

Differences

	hosts & range
	feed up
	OW in leader
	attack height 2-5 m
	typical attack rate 5%
	hazard related to BEC (warmth) & density
	JS

Source: http://www.fs.fed.us/r1-r4/spf/fhp/field_guide/images/fig156.jpg

General Biology of Terminal Weevils in BC

Order: Coleoptera

complete metamorphosis (compare young vs. adult of terminal weevil vs. sap suckers)

chewing mouth parts (again, compare to sap suckers)

Adults feed on terminal leader - no significant damage / larva feed under bark and are damaging

Simplified life cycle

adult feeds on leader (chomps a hole in the bark)

female lays egg then 'deposits a fecal cap' (polite way of saying ¢®^¶) on the egg site (apparently they are not potty trained)

eggs hatch in a couple of weeks

larva feed on phloem of leader

pupate inside leader

adult emerges, feeds on twigs, OW in duff, re-emerge in spring

Spruce Terminal Weevil (a.k.a. White Pine Terminal Weevil)

In natural stands this can be a 'rare' insect pest - small openings, shaded conditions, small leaders. However, in the 1970's we established large plantations of S ... which meant large food source in a warm area (more about heat sums later)

Hosts & Range

	In BC - Ss, Se, Sw (Sb, Pl)
	Out east, (who cares ... well ...) - pines (white, red, jack, scots) and spruce (white, red, norway, colorado, black)

Map of Weevil Distribution in North America

Source: http://www.pfc.forestry.ca/entomology/weevil/about_e.html

Note: not on Queen Charlotte Islands

Life Cycle

Adults

feed on leaders just below terminal bud

lay eggs and cover with fecal cap in late spring (May-June)

up to 100 eggs per leader

after laying eggs adults can resume feeding (on terminals and laterals) and a life free of kids

adults can live up to 4 years

Eggs hatch in ~ 2 weeks

Larvae

are stout, legless yellow-white grubs, 0.6-1.2 cm

"Tastes like chicken"

L1 feed independently, but later they form a feeding ring and feed in summer months

this girdles the leader

larva feed downwards

kills 2 (3) years of growth

Pupae

are white and resemble the adult

they encase themselves in a "chip cocoon" in the sapwood

Adults

emerge in late summer (rusty brown / black) and are about 1 cm long

are teneral adults until maturation feeding

OW in duff

in spring they walk or fly to new host tree

Life Cycle Diagram from PFC

Life History from FPC Guidebook

Tree Response

	resin (more on this later) - attempt to 'pitch out' the attack
	lateral assumes dominance ... leads to fork or crook Roughly 40% - no damage 10% - minor scar 45% - minor fork / crook 5% - major fork / crook Actual impact depends on site productivity good sites - trees 'over grow' the defects more often poor sites - greater damage

Population Dynamics

Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/weevil/figure3.htm

attack starts at about 5 years (~1/2 m tall)

peaks at 15 - 30 years (2 - 10 m tall)

outbreak period ~ 15 years

fluctuates with

weather

enemies (parasitoids & predators)

Photo of Lonchaea corticis fly larvae preying on the white pine weevil larvae

Source: http://www.pfc.forestry.ca/entomology/weevil/mortality_e.html

The larvae of the Lonchaea corticis fly (above) prey on the white pine weevil larvae

competition for leaders

outbreak % higher on better sites (bigger leaders)

then population declines

slower growth on spruce (smaller leaders)?

duff (OW site) more shaded?

most trees attacked within 5 m of nearest attacked tree

Signs & Symptoms

leaders in spring - feeding punctures with droplet of resin

leaders previously attacked

red foliage

Sheppard's crook

top 2-3 years growth dead

older attack

crease, fork, crook staghead

Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/weevil/figure4.htm

inside leader

spring/summer of current attack - larva / pupa

older attack - exit holes, chip cocoons

adult - rusty brown with cream splotches

Source: http://www.for.gov.bc.ca/tasb/legsregs/fpc/fpcguide/weevil/table3.htm

Sheppard's Crook

Source:http://1.bp.blogspot.com/_8xC9bwq6AVU/SfGU0pArUYI/AAAAAAAAH9c/2hQ_vhh1axM/s400/wpw5.jpg

feeding larva

Source: http://www.forestry.ubc.ca/fetch21/FRST308/lab4/pissodes_strobi/larvae2.jpg

Chip cocoons

Source: http://www.fs.fed.us/r1-r4/spf/fhp/field_guide/largeimages/fig158-x.jpg

Exit Holes

Source: http://www.fs.fed.us/r1-r4/spf/fhp/field_guide/images/fig155.jpg

Adult

Source: http://www.forestryimages.org/images/192x128/1306048.jpg

Adult

Source: http://www.forestryimages.org/images/192x128/1306048.jpg

Tree Resistance

	repellants - (antixenosis) terpenes at high concentrations deter feeding and oviposition
	juvenile hormone - (antibiosis) causes ovary atrophy (remain small and undeveloped), female cannot lay eggs
	traumatic resin - (antibiosis) has mono-terpenes (makes the resin more fluid and better able to 'soak' the egg site)
	we are breeding for these traits

Damage

	deformity (= value)
	growth loss (= volume)
	avenue for decay (= volume)
	loss of preferred species (= value)
	deformity ... remember

Roughly

40% - no damage

10% - minor scar

45% - minor fork / crook

5% - major fork / crook

Actual impact depends on site productivity

good sites - trees 'over grow' the defects more often

poor sites - greater damage

growth loss (table of volume loss related to attack % and attack duration)

Attack % / Year	10 Years	20 Years	30 Years	40 Years
10% / yr	5%	10%	15%	20%
20% / yr	15%	20%	25%	30%
30% / yr	20%	30%	35%	40%
40% / yr	20%	30%	35%	40%

ball park figures: likely 15-25% volume loss, but could be in the range of 5 - 40%

Hazard Rating

2 methods:

field observation & survey - = actual hazard - but some areas have little recorded history "new watersheds"

ecosystem (BEC = biogeoclimatic zones) - see Tree Doctor

theoretical method = HEAT SUM

coast - 888 degree days (above 7.2 celcius)

interior - 785 degree days (above 7.2 celcius)

degree days = [ (max temp + min temp) / 2 ] - 7.2

	calculate for each day and sum for year
	e.g. 18 max and 8 min ... 5.8 degree days

heat sum is related to latitude and elevation

Management

Hazard Rating - Coast

	none - (QCI) - no restrictions
	low - (north coast & north end of VI) - no restrictions
	medium - (outer west coast of VI) - < 20% Ss & ensure MSS met with other species
	high - elsewhere - <10% Ss & ensure MSS met with other species

Brushing

brush = shade ... competition for conifers, but lower weevil attack

Interior

	short brush (willow) - no treat, as brush will do 'less damage' than weevil
	tall brush (aspen) - B&W and live with weevil

Coast

if Ss important for stocking then need to think (figures below are 'rough')

Age	Low attack	High Attack
< 15 yr	<10% attack - B&W likely OK	>10% - delay B&W
>15 yr	<20% attack - B&W likely OK	> 20% - delay B&W

Fertilize - are you nuts?

Spacing

	dense stands are less affected by weevil (smaller leaders, more shaded duff?)
	therefore delay spacing until after pop'n subsides

Prune?

	done after JS
	seems to have no effect on infestation levels
	if you have lotsa $$$ then I guess you could ...

Rehabilitation - means cutting all the trees down and starting over ... pretty drastic

only if meet these criteria:

need Ss to meet MSS (NSR without Ss)

attack rate high (>30%)

tree condition (from intense surveys):

	for stems >5m - >50% with major defect - then consider rehab
	for stems <5m - most trees trees <2/3's ht of 'normal' Ss (e.g. severely stunted) - consider rehab

there are no other high resource value (e.g. wildlife, fisheries) that would be impacted with treatment

Direct Control

leader clipping

	3x's per year for 5 consecutive years (adult lives up to 4 years)
	too labor intensive and $$$$

stem injected insecticides

	can give 2 years protection
	under development

resistant stock

under development

remember

	repellants - (antixenosis) terpenes at high concentrations deter feeding and oviposition
	juvenile hormone - (antibiosis) cause ovary atrophy (remain small and undeveloped), female cannot lay eggs
	traumatic resin - (antibiosis) has monoterpenes (makes the resin more fluid and better able to 'soak' the egg site

Pine Terminal Weevil

Differences are highlighted

Hosts & Range

	Pl & Pj
	Interior, following hosts

Biology

eggs laid in emerging leader

larva feed up

therefore only current growth is lost

OW as larva/pupa in pith of leader - high mortality rate

adults emerge next summer

	if emerge in early summer ... feed, mate, eggs, OW in duff
	if emerge in late summer ... feed, OW in duff
	adults live for 2 (+?) years

attack height is 2 - 5 m (vs. 1 - 12 m)

typical attack is 5% of leaders (25% is maximum)

Signs & Symptoms

Hazard

related to BEC zone (warmth) and density

Hazard	BEC Zone	Density (sph)
High	IDF & MS	<1400
Moderate	MS	1400 - 2000
Low	MS ESSF	>2000 >1800

note that hazard is higher with warmth and lower density

Management

JS - wait until 5+ m tall and attack < 10%

if attack > 10% then

	delay, or
	post spacing density should be higher

It is obvious that the pine terminal weevil is ... (what?)